Things that interfere with blood tests?

Antibiotics and such herbs aside, what else might negatively impact the results? Smoking is pretty obvious?

Are there any steps to decrease the odds of a false negative, like strengthening the immune system?

Also I bought serrapeptase but havent really used it, made me feel horrible, I read that it could be used to dissolve biofilm or cysts... I honestly don't rememberwhich, maybe both.

Would it be a good idea to take this for a week or so before getting the blood work done?

I think you're supposed to take olive leaf extract or something similar to stimulate your immune system. The blood tests are looking for antibodies, so antibiotics would actually help you get a positive test.

Serrapeptase is used for biofilm, but I don't think it would affect blood test results.